Altcoins are not a threat to Bitcoin. If there is an altcoin that performs better than Bitcoin and surpasses Bitcoin, then I welcome such altcoin, I don't see anything bad into that, we are not married to Bitcoin after all.
There is not really any threat if we keep in mind that Bitcoin's code can be changed at any time if there is a full approval from the community. If any altcoin advances, Bitcoin can advance too.
Yes, if there is an altcoin or some currency that can beat bitcoin, I would welcome it too. I also think there is nothing to be ashamed or afraid of if it happens, I even hope it can happen sooner. Because after all, they are all tools and their purpose is to serve humanity, there is no reason to fear or seek to hinder that development.
But looking at the current situation, I tend to agree with everyone that there will be no altcoin that is good enough and can surpass bitcoin to dominate the crypto industry in the near future. Looking at the altcoin market is like a gambling place, there is no serious development that shows they are trying to create something useful like what bitcoin gives us.